Several aspects of the control of gene action in the development of viruses are to be investigated. The proposed experiments involve two large bacterial viruses, SPO1 and T4, and their respective hosts, B. subtilis and E. coli. RNA polymerase modification and function during SPO1 infection will be further analyzed. RNA polymerase-binding peptides have been separated and their functions will be analyzed in terms of the mechanism of promoter complex formation, RNA chain initiation and, possibly, termination. Transcription units will be mapped. The reciprocal relation of host and viral transcription will be analyzed in terms of RNA polymerase changes. The connection between replication and late gene expression in T4 virus infection will be further analyzed. An in vitro system for T4 late RNA synthesis will be further analyzed. Studies on the formation of RNA polymerase-DNA initiation complexes involving a eucaryotic RNA polymerase will be initiated.